coolant leak weirdness

[Woodbutcher]

About a month ago I had my transmission fluid changed at the local Grease Monkey. I mention that because I thought this might have been due to them overfilling the coolant since they top off fluids as part of their service. A week or so later I found a little coolant under my Ex (98 XLT 5.0L AWD), passenger side, front. I found coolant dripping slowly from the passenger side edge of the radiator. No overheating, but apparently it must have leaked from the overflow tank as the fluid level was low. Over about a week I would find a little bit of coolant - maybe a few ounces at most at any one time - under the vehicle in the morning. Less in colder weather, more in warmer, but at the time it was not cold enough out to need to run the heater. Didn't appear to leak while the engine was running, just when stopped, but then it was a slow leak so it may have leaked while running as well. I checked the radiator and the level wasn't low at the time. After about a week there were no more puddles underneath, and the temp was steady normal operating temp. Stayed apparently normal for several weeks. This week I drove up to Ft. Collins, which was longer than my usual highway drive, but only about an hour. On my return trip I noticed the temp started rising to the high end of the range, so I slowed down and stopped at a gas station where I checked the radiator and it was low, so I added about half a gallon. No problem after that, and still no visible leak. The only other thing was that in the last couple of weeks my heater has been intermittently blowing cold air, then warm, then cold - fluctuating. From what I read in other threads, maybe the thermostat housing and/or the narrow hose from the overflow tank could be the culprit, but what do you think? And if that was the case, could it affect the heater that way, or am I looking at a heater core problem? Leak was at the front of the engine compartment, not back by the firewall.

 

[OneLever]

I found coolant dripping slowly from the passenger side edge of the radiator. No overheating, but apparently it must have leaked from the overflow tank as the fluid level was low.

The seam between the plastic tank and aluminum core of the radiator on my 5.0L failed last winter. I was loosing coolant slowly from what appeared to be near the upper radiator hose connection. After making sure it wasn't the connection, which you should do also, I replaced the radiator and fixed the leak. I was able to get away with it for some time by constantly adding coolant, but in your case it is beyond that. If your engine overheats you're looking at a blown head gasket and possible head damage.

The overflow reservoir is closer to the passenger side middle. The heater core is buried in the passenger side of the firewall and has a drain near there. The thermostat is near the top center of the engine. None of those sound like a source of your leak.

The only other thing was that in the last couple of weeks my heater has been intermittently blowing cold air, then warm, then cold - fluctuating.

You likely have air pockets in the coolant system from the leak which will disrupt the system. If coolant is leaking out it stands to reason that air is seeping in.

Here is a related post of the specs my old radiator had: Link 1
If you have never removed the upper radiator hose it will likely need to be cut off. Here is link on that: Link 2
While you're in there you might as well replace the thermostat and water pump bypass hose: Link 3, and full thread of Link 2.

You can buy UV dye and light kits for around $20 to make sure you know where the leak is coming from. Radiator, thermostat, bypass hose, new upper radiator hose, Permatex Right Stuff, and 3 gallons of coolant all together will run you around $250-$290. You can use the coupon code "P20" at Advance Auto Parts to get 20% off your total order.

I have no affiliation with them nor am I a professional. I'm just trying to save you some of the time and hassle I went through.

 

[Woodbutcher]

Thanks OneLever. Makes sense about the air in the system, and the location of the leak. Not sure why I haven't seen any leaks under the vehicle since the initial leak, and also since I filled the radiator on my trip there have been no puddles. It never overheated, but the gauge was climbing higher than normal on that one trip. Anyway, sounds like the first issue is finding the leak so I'll start there.

 

[OneLever]

You're welcome. I agree that you should try to pinpoint it first. I've never used the UV kits but understand the principle. Based off that I'd say it may be easier to use one at night time where the only illumination is the UV light making the dye visible.

Please update us when you find and fix your issue.

 

[1AJeremyD]

You're welcome. I agree that you should try to pinpoint it first. I've never used the UV kits but understand the principle. Based off that I'd say it may be easier to use one at night time where the only illumination is the UV light making the dye visible.

Please update us when you find and fix your issue.

I've always had good luck with either shade or low lit area. I don't think night would be a good idea because of the area you live in lol. I know here in Mass its been pretty cold to be doing work on anyones car if your outside and then add dark = frustration all night long.:thumbdwn::frustrate

 

[OneLever]

Let me amend that: night time with a headlamp. I never work in pitch black darkness. I always wear a headlamp because it's convenient and places the source at the most optimal location (near your eyes) and leaves your hands free. Fumbling around in pitch black with the engine running is a recipe for disaster.

 

[TONERDIVER]

A pressure test is much easier than a dye test. You dont need any special lights to find uv dye. Just remove rad cap,pump up the cooling system with tester and you will finf the leak.